This invention relates to programmable semiconductor memories and, more particularly, to charge pumps for such memories.
Some programmable memory devices, such as electrically erasable programmable read on memories (EEPROMs) and flash memories, require relatively high programming voltages. The programming voltages may be significantly higher than the supply voltage available on conventional integrated circuits. Thus, a boosted voltage must be supplied to a selected address line to be programmed. That voltage may be from a few volts to over ten volts above the supply voltage Vcc. At the same time, unselected address lines should not draw DC current to the greatest possible extent.
A charge pump may be provided to increase the voltage provided by the supply voltage to the higher voltage needed for programming. The demands on the charge pump have increased as the availability supply voltages have dropped dramatically. Even with lower supply voltages, the need still exists for a relatively high programming voltage. A charge pump is needed that can pump a relatively low supply voltage, such as a supply voltage of 1.5 volts or less, up to the levels needed to program certain semiconductor memories.
Thus, there is a need for better charge pumps for programmable semiconductor memories.